Fluororesin films have such properties that they excel not only in resistance to strong acids, strong alkalis and organic solvents but also in heat resistance and that they have extremely small friction coefficients to exhibit good slipperiness; in particular, tetrafluororesins typified by polytetrafluoroethylene (hereinafter abbreviated as PTFE) excel in thermal and chemical stability and friction characteristics (with slipperiness being particularly good), as well as excel in biocompatibility; hence, they are applied in various fields of medical equipment.
Patent Document 1 describes a guide wire comprising dissimilar metals welded together to form a wire body, with the weld joint being covered with a coating layer that is formed of a fluoropolymer.
However, PTFE, because it excels in thermal and chemical characteristics, has only poor thermal fusing and bonding properties and, particularly in the case of bonding to metals, it is subjected to a special surface treatment; take, for example, the case of applying a PTFE coating to provide improved friction characteristics; in one of two special methods currently adopted, the surface of PTFE is activated by defluorination with a metallic sodium/liquid ammonia solution and bonded with an epoxy adhesive; in the alternative method, a tetrafluoroethylene/hexafluoropropylene copolymer resin (FEP) is used as an adhesive during the application of heat and pressure.
Stainless steel and other metal wires are employed as a guide wire for assisting in the insertion of a catheter; however, the large friction coefficient of metals causes difficulty in steering the guide wire to be smoothly inserted into the body and medical settings need an improvement in this steerability. A potentially promising technique is to coat the metal wire with PTFE of low friction coefficient; however, because of the various problems with this technique, e.g., inability of certain kinds of metal wires to be heated at high temperature, difficulty in applying a uniform coating to thin metal wires by this technique, and the aforementioned poor adhesion between PTFE and metals, the application of PTFE coating to metal wires has yet to be commercialized.
Patent Document 2 describes a guide wire having a lubricating layer that is formed of a hydrophilic polymeric substance that develops lubricating properties when it is wet.
In addition, Patent Document 3 describes a coated product comprising a material to be coated and a coating layer covering at least that portion of the material to be coated which is to be contacted with body fluid, the coating layer comprising at least fine particles of a fluorine-containing polymer and a non-fluorine-containing polymer.    Patent Document 1: JP 2004-181089 A    Patent Document 2: JP 2002-28249 A    Patent Document 3: WO 98/38258